1 Einstein's Legacy: General Relativity, our Best Description of the Universe Barry C. Barish Caltech LLNL Science Day 23-May-05

2 Annus Mirabilis  In 1905, Albert Einstein wrote five revolutionary scientific papers.  These papers altered our understanding of the nature of light, proved the existence of atoms and molecules, and established the concept of special relativity.

3 Gravity a fundamental force

4 Universal Gravitation  Solved most known problems of astronomy and terrestrial physics »eccentric orbits of comets »cause of tides and their variations »the precession of the earth’s axis »the perturbation of the motion of the moon by gravity of the sun  Unified the work of Galileo, Copernicus and Kepler unified.

5 But, what causes the mysterious force in Newtons theory ? Although the equation explains nature very well, the underlying mechanism creating the force is not explained !

6 After several hundred years, a small crack in Newton’s theory ….. perihelion shifts forward an extra +43”/century compared to Newton’s theory

7 G  = 8   General Relativity the essential idea  Overthrew the 19 th -century concepts of absolute space and time  Gravity is not a force, but a property of space & time » Spacetime = 3 spatial dimensions + time » Perception of space or time is relative  Concentrations of mass or energy distort (warp) spacetime  Objects follow the shortest path through this warped spacetime; path is the same for all objects

8 General Relativity Einstein theorized that a massive object warps the surrounding space

9 General Relativity Smaller objects travel through space that is warped by larger objects

10 A new prediction of Einstein’s theory … Light from distant stars are bent as they graze the Sun. The exact amount is predicted by Einstein's theory.

11 Confirming Einstein …. A massive object shifts apparent position of a star bending of light Observation made during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster

12 Einstein’s Cross The bending of light rays gravitational lensing Quasar image appears around the central glow formed by nearby galaxy. The Einstein Cross is only visible in southern hemisphere.

13 Gravitational Waves ?

14 A Conceptual Problem is solved ! Newton’s Theory “instantaneous action at a distance” Einstein’s Theory information carried by gravitational radiation at the speed of light

15 Russel A. Hulse Joseph H.Taylor Jr Source: Discovered and Studied Pulsar System PSR with Radio Telescope The The The Evidence For Gravitational Waves

16 Radio Pulsar Neutron Star

17 The evidence for gravitational waves Hulse & Taylor   17 / sec Neutron binary system separation = 10 6 miles m 1 = 1.4m  m 2 = 1.36m  e = period ~ 8 hr PSR Timing of pulsars Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period

18 “Indirect” evidence for gravitational waves

19 The Nature of Gravitational Waves Ringdown Inspiral Merger Compact Binary Inspiral

20 The effect of a gravitational wave passing through space …

21 Direct Detection Detectors in space LISA Gravitational Wave Astrophysical Source Terrestrial detectors LIGO, TAMA, Virgo,AIGO

22 stretch and squash in perpendicular directions at the frequency of the gravitational waves Leonardo da Vinci’s Vitruvian man I have greatly exaggerated the effect!! If the Vitruvian man was 4.5 light years high, he would grow by only a ‘hairs width’

23 laser Gravitational Wave Detection Laser Interferometer free masses h = strain amplitude of grav. waves h =  L/L ~ L = 4 km  L ~ m

24 The Detection Technique  Laser used to measure relative lengths of two orthogonal arms As a wave passes, the arm lengths change in different ways…. …causing the interference pattern to change at the photodiode  Arms in LIGO are 4km  Measure difference in length to one part in or meters

25 How Small is Meter? Wavelength of light ~ 1 micron One meter ~ 40 inches Human hair ~ 100 microns LIGO sensitivity m Nuclear diameter m Atomic diameter m

26 LIGO Laser Interferometer Gravitational-wave Observatory Hanford Observatory Livingston Observatory Caltech MIT

27 LIGO Livingston, Louisiana 4 km

28 LIGO Hanford Washington 4 km 2 km

29 What Limits LIGO Sensitivity?  Seismic noise limits low frequencies  Thermal Noise limits middle frequencies  Quantum nature of light (Shot Noise) limits high frequencies  Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals

30 Evolution of LIGO Sensitivity

31 An earthquake occurred, starting at UTC 17:38. From electronic logbook 2-Jan-02 Detecting Earthquakes

32 Detect the Earth Tide from the Sun and Moon

33 Astrophysical Sources signatures  Compact binary inspiral: “chirps” »NS-NS waveforms are well described »BH-BH need better waveforms »search technique: matched templates  Supernovae / GRBs: “bursts” »burst signals in coincidence with signals in electromagnetic radiation »prompt alarm (~ one hour) with neutrino detectors  Pulsars in our galaxy: “periodic” »search for observed neutron stars (frequency, doppler shift) »all sky search (computing challenge) »r-modes  Cosmological Signal “stochastic background”

34 Directed Pulsar Search 28 Radio Sources

35 Detection of Periodic Sources  Known Pulsars in our galaxy  Frequency modulation of signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes.  Amplitude modulation due to the detector’s antenna pattern. NEW RESULT 28 known pulsars NO gravitational waves e < – (no mountains > 10 cm ALL SKY SEARCH enormous computing challenge

36  A maximum-sensitivity all-sky search for pulsars in LIGO data requires more computer resources than exist on the planet.  The world’s largest supercomputer is arguably »A $599 computer from Radio Shack is a very powerful computational engine. »Currently runs on a half-million machines at any given time.  With help from the developers, LIGO scientists have created a distributed public all-sky pulsar search.

37 Usage Already have about 35K Users 20x LIGO computing capacity

38 LIGO Pulsar Search using home pc’s BRUCE ALLEN Project Leader Univ of Wisconsin Milwaukee LIGO, UWM, AEI, APS